1. Field of the Invention
The present invention relates to an air-intake device for an internal combustion engine, in which a function for adjusting an amount of an intake-air volume and a function for generating a desired air stream are included.
2. Description of Related Art
An example of an air-intake device is disclosed in JP-A-7-269375. In this device, a rotary-type throttle valve rotatable around a shaft supporting a diametric center of the throttle valve is disposed in an intake air passage. An amount of air supplied to an internal combustion engine is controlled according to an opening-degree of the rotary-type throttle valve. An additional air passage for a low air volume, corresponding to a region of a low opening-degree of the throttle valve, is provided at an upstream portion of the throttle valve in order to control an amount of air more precisely in a low air volume region. The rotary-type throttle valve in this device, however, does not generate a desired airflow directed toward an intake port of an engine cylinder. If it is necessary to generate the airflow, an airflow control valve has to be additionally provided at a downstream portion of the throttle valve, thereby increasing a manufacturing cost of the device.
Another example of this kind of device is proposed in JP-A-9-222063. In this device, an airflow control valve rotatable around its center axis is provided downstream of a throttle valve that controls an amount of air supplied to an engine. Further, a guide-groove for generating a high speed airflow when the airflow control valve is closed is provided along a wall of an intake air passage. The airflow control valve and the guide-groove in this device, however, do not has a function for precisely controlling an amount of air at a low air volume region though the airflow is generated. Further, since the airflow control valve is rotatable around its center axis, air also flows through an opening formed at an opposite side of the guide-groove when the airflow control valve is opened. Accordingly, the guide-groove cannot generate a desired airflow effectively.
A conventional throttle valve is usually made rotatable around its center axis, and intake air flows though openings at both sides of the throttle valve when it is opened. Therefore, it is difficult to precisely control an amount of intake air at a region where a volume of the intake air is low.